Prothrombin is a thrombin precursor protein having a molecular weight of about 72,000 which is produced in the liver and is also called “blood coagulation factor II”. Limited proteolysis of prothrombin in vivo with the complex of activated factor X, activated factor V, phospholipids, and calcium ions results in conversion into thrombin. Thrombin is a serine protease that converts fibrinogen to fibrin by limited proteolysis in the blood-clotting reaction as well as an important protein involved in hemostasis, wound healing or the like. Therefore, the thrombin is used not only as a hemostatic agent or blood test reagent in the clinical field, but also as a reagent for study in the molecular biology field, etc.
Since a large amount of thrombin is present in the plasma, thrombin as a preparation or reagent is mainly prepared by using the plasma from human or bovine as a raw material. However, there is a risk such that infectious materials such as hepatitis virus, human immunodeficiency virus, and abnormal prion are mixed in those raw materials. Further, the plasma is a naturally-occurring raw material and thus a difference between the production lots causes a problem. Therefore, the methods for producing thrombin from the prothrombin or prethrombin produced by the recombinant DNA technique using Escherichia coli or mammalian cells have been recently studied and developed (Japanese Patent Application Laid-Open (JP-A) No. 2002-306163, US 2004/197858, and US 2009/137001).